The present invention relates to thermoplastic sheet products and to a method and apparatus for their manufacture. More particularly, the invention is related to a method and apparatus for perforating a continuous sheet or film of thermoplastic material to produce film having increased strength and reduced edge curl.
Perforated thermoplastic sheets have many useful applications. Perforated sheets are used in gardening and farming to prevent the growth of grass and other weeds while permitting more moisture to be transmitted through the sheet to the soil beneath the sheet. Perforated sheets are also used for making disposable baby diapers. U.S. Pat. No. 3,814,101 discloses diapers employing perforated thermoplastic sheets which permit the flow of liquid in the direction of the absorbent material in the diaper but substantially reduce the possibility of flow in the opposite direction.